RE: [T3] Turn Signal & Headlamp

["Jim Adney" <jadney@vwtype3.org>]

On 1 May 2001, at 15:30, Diana Howlett wrote:

> This is the first oil change since I owned the car.  I loosened the center
> drain plug and then loosened the six cap nuts surrounding the plug.  The
> drain plug came out fine and after letting the oil drain for about 20
> minutes, I proceeded to remove the drain cover plate to get to the strainer
> assembly.  Three of the six cap nuts wouldn't separate from the bolts they
> were attached to.  Those aren't supposed to come out are they?  I didn't
> find much literature surrounding these bolts in my manuals.  So I just
> replaced the gaskets and put everything back the way it came out.  However
> one of the bolts is stripped, as it won't tighten up.  Is there a specific
> torque on the six cap nuts.  There was torque specified for the drain plug,
> but not the six caps. 

I'm afraid this is a rather common problem with our old cars by 
now. These are 6mm bolts set into cast magnesium; the torque on 
them should be minimal. I tighten them with my hand on the head 
of the ratchet to keep me from overtightening.

There are several causes of this problem. VW used a cap nut here 
to prevent a leak path thru the threads. This means that the tapped 
hole is a blind hole and the length and depth of things is critical. If 
you leave out a gasket, including the small metal ones that go 
under the cap nuts, then the stud goes deeper into the cap nut and 
may seize up.

Then there is the aftermarket cap nut problem. It is difficult to tap 
all the way to the bottom of a cap nut, the OE ones were done 
pretty well, but the cheap aftermarket ones are often very poor. I 
end up spending a long time with a special tap cutting these as 
deep as they need to be to spin freely all the way as far as they 
need to. 

Even OE cap nuts can seize on the studs if you get sand in the 
threads, so you need to be careful with your hardware when you 
change the oil.

The best repair is an M6 x 1 Helicoil locking insert, but the repair 
kit may cost more than you want to spend. If you drove over here I 
have a special pilot I made to drill and tap these for the Helicoils 
while keeping the inserts straight and in the correct bolt pattern.

The best solution I have seen is to install hex head bolts from the 
inside of the case while doing an overhaul. This has to be done 
carefully to get the exposed length of thread exactly right. Even 
then I Helicoil any stripped threads before installing the bolts.


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Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
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